The studies designed in this application are intended to equip the principal investigator, Dr. Michael Jurczak, with the technical and scientific expertise necessary to become an independent investigator exploring the regulation of mitochondrial turnover and its role in maintaining mitochondrial integrity and function. Specifically, Dr. Jurczak will develop methodology to measure rates of mitochondrial turnover in mice in vivo and apply genetic and pharmacological approaches to understand how this process is regulated. Because impaired mitochondrial function is strongly associated with the degree of insulin resistance in both young and old human subjects, these studies have the potential to elucidate a mechanism by which mitochondria accumulate damage and contribute to our understanding of the pathogenesis of type 2 diabetes. Also, because our current understanding of mitochondrial turnover comes from studies in cell culture, these would be the first studies to address the role of what are thought of as key players in the regulation of mitochondrial turnover - Parkin, mitochondrial uncoupling and activation of autophagy - in vivo. To this end, the following studies are proposed: 1) evaluate the importance of Parkin, mitochondrial uncoupling and autophagy to the regulation of mitochondrial turnover in vivo by validating and applying a novel stable isotope approach in mice; 2) evaluate the role of Parkin in liver using a novel model of conditional Parkin deletion. The above work will be carried out by Dr. Michael Jurczak under the supervision of Drs. Gerald Shulman, Gerald Shadel and Akiko Iwasaki in the Department of Internal Medicine, Section of Endocrinology at Yale University. This application was carefully designed to facilitate Dr. Jurczak's transition to Assistant Professor at the end of the three year award. Through this award, he will broaden his technical and scientific knowledge base, generate data and acquire new skills necessary to succeed as an independent investigator. These goals will be met through his engaging directly in the proposed research, by meeting regularly with his advisory committee, completing proposed coursework and attending specific scientific meetings. The Department of Internal Medicine at Yale provides an ideal environment to pursue the proposed training and Dr. Shulman and the Department are deeply committed to Dr. Jurczak's success.